Preliminary investigation on rats afflicted with hereditary degeneration (dystrophy) showed that electrophysiologically measured visual capacities survive to a surprising degree when the great majority of visual cells has disappeared. This includes the mass potentials of the primary visual cortex in response to diffuse light stimuli and in response to black-white gratings. Impulse activity of optic nerve axons in response to spots of light provide unequivocal evidence of retinal photoreception at a stage of advanced degeneration. The number of units of fast and intermediate conduction speeds is little decreased and their receptive field size and antagonistic organization differs little from normal. It is proposed that surviving cone-like cells, lacking inner and outer segments, are the photosensitive elements. It is planned to obtain data on the number of functional information channels and on the receptive field organization of retina and lateral geniculate body in relation to histological measurements.